Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/8744#discussion_r39583969
--- Diff:
yarn/src/main/scala/org/apache/spark/scheduler/cluster/YarnExtensionService.scala
---
@@ -0,0 +1,198 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.scheduler.cluster
+
+import java.io.Closeable
+import java.util.concurrent.atomic.AtomicBoolean
+
+import org.apache.hadoop.service.AbstractService
+import org.apache.hadoop.service.Service.STATE
+import org.apache.hadoop.util.ShutdownHookManager
+import org.apache.hadoop.yarn.api.records.{ApplicationAttemptId,
ApplicationId}
+
+import org.apache.spark.util.Utils
+import org.apache.spark.{Logging, SparkContext}
+
+/**
+ * An extension sservice that can be loaded into a Spark YARN application.
+ * A Service that can be started and closed (==stop).
+ *
+ * The `close()` operation MUST be idempotent, and succeed even if
`start()` was
+ * never invoked.
+ */
+trait YarnExtensionService extends Closeable {
+
+ /**
+ * For Yarn services, SparkContext, and ApplicationId is the basic info
required.
+ * This operation must be called before `init`
+ * @param sc spark context
+ * @param appId YARN application ID
+ * @param attemptId YARN attempt ID if known. Otherwise, `None`.
+ */
+ def start(sc: SparkContext,
+ appId: ApplicationId,
+ attemptId: Option[ApplicationAttemptId]): Boolean
+}
+
+
+/**
+ * Class which loads child Yarn extension Services from the configuration,
+ * and closes them all when closed/stopped itself.
+ *
+ * It extends YARN's `AbstractService` to pick up its state model, and
adds an alternate entry
+ * point for actually configuring and starting the service.
+ *
+ * An instance may be configured to register a shutdown hook. This
addresses the issue in
+ * which a spark context is not always closed in an application,
especially a `yarn-client`
+ * application. The shutdown hook allows services an opportunity to
perform any final
+ * actions their `Service.stop` invocations trigger.
+ */
+private[spark] class YarnExtensionServices extends
AbstractService("YarnExtensionServices")
+ with Logging {
+ private var services: List[YarnExtensionService] = Nil
+ private var sparkContext: SparkContext = _
+ private var appId: ApplicationId = _
+ private var attemptId: Option[ApplicationAttemptId] = _
+ private val started = new AtomicBoolean(false)
+ private var registerShutdownHook = false
+ private var shutdownHookPriority = 0
+
+ /**
+ * This is the routine to optionally be registered as a shutdown hook.
+ * It logs the invocation and then calls the `close()` method to stop the
+ * service instance. It is public to aid in testing.
+ */
+ val shutdownHook = new Runnable {
+ override def run(): Unit = {
+ logInfo(s"In shutdown hook for $this")
+ try {
+ stop()
+ }
+ catch {
--- End diff --
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